Supply system for a liquid

ABSTRACT

A supply system for liquid including a liquid tank and a liquid supply line forming a passage for the liquid from the tank to an outlet of the supply system. The supply line includes at least one part configured to form at least one gas pocket communicating with the passage to take up a change of volume of the liquid in event of freezing. Such a system can be used in a selective catalytic reduction system (SCR).

The present invention relates to a system for supplying a liquid whichis liable to solidify in case of frost, in particular for a vehicle,such as an internal combustion engine exhaust gas reducing agent.

To meet the requirements concerning emissions from vehicles, inparticular heavy goods vehicles, it is necessary to reduce the amount ofoxides of nitrogen NO_(x) discharged in the atmosphere. The methodgenerally proposed is to use SCR (Selective Catalytic Reduction) whichallows for reduction of the oxides of nitrogen by injecting a reducingagent, generally ammonia, into the exhaust system. This ammonia mayoriginate from the thermolytic decomposition of a solution of an ammoniaprecursor, the concentration of which may be the eutectic concentration.An ammonia precursor such as this is generally a solution of urea.

The vehicles are generally equipped for this purpose with a tankcontaining a urea solution, a device for metering the amount of urea tobe injected into the exhaust line and a device for supplying the ureasolution to the device for metering the amount of urea to be injected.In general, the supply device comprises a supply line, a pump and afilter.

The supply line generally feeds the solution to an injector at one endof the line, whereas the opposite end emerges into the tank. The pump islocated inside or outside the tank and a pressure regulation is foreseento regulate the pressure of the reducing agent provided to the injector.

To prevent the components of the supply system, and in particular thosementioned above, from being damaged following the solidification of theaqueous urea solution in freezing conditions (generally an eutectic with32.5% by weight of urea, freezes at −11° C.), it is advantageous toperiodically purge the supply line as well as the components locatedover this supply line.

Various systems for performing such a purge have been provided in theprior art.

As described for example in applications WO 2006/064028 and WO2009/007405 in the name of the applicant, this purge can take place byusing compressed air or by sucking the exhaust gases or air through aninjector, either by using a 4/2-way valve or by reversing the rotationaldirection of the pump.

It is also preferable to equip the system with a non-return device(preferably a bell/siphon combination) that prevents liquid (reducingagent) from entering into the purged elements once the pump has beenstopped, while allowing the supply of liquid to the supply line when thepump operates/starts in the supply mode.

EP 1 664 713 and EP 1 339 956 propose, on the other hand, to protectonly a particular component of such a system, namely the pressuresensor, either via additional bellows bordering a compressible volumewhich takes up a change of volume of the reducing agent in the event offreezing (EP 1 664 713) or via a valve body that can carry out acompensating movement in a line to increase the volume thereof in theevent of freezing of a reducing agent located in this line (EP 1 339956).

It appears from the foregoing that substantial modifications arenecessary to protect the supply system or a component thereof againstfrost and might limit the protection to a particular component.

The present invention aims to solve these problems by proposing a supplysystem which is completely protected against frost in a manner that issimple, effective and reliable.

For this purpose, the present invention proposes a supply system for aliquid, comprising a liquid tank and a liquid supply line forming apassage for the liquid from the tank to an outlet of the supply system,characterized in that the supply line is provided with at least one partdesigned to form at least one gas pocket communicating with said passageto take up a change of volume of the liquid in the event of freezing.

Thanks to these provisions, the supply line as well as the componentslocated over this line are protected against frost without any need topurge the supply line and with means which are very simple and easy toimplement (modification of the supply line) and do not pose any problemof reliability.

Moreover, such a gas pocket, preferably an air pocket, provides animproved pressure regulation in the case of an exhaust gas reductionsystem, by damping the pressure pulses and reducing the pressure rangeduring injection.

In addition, such a system does not call for particular conditions as tothe location of the means for protecting it against frost (the gaspocket in practice).

By gas pocket, is meant a recess storing gas, preferably air, the volumeof which is defined/dimensioned considering the expansion volume of theliquid in freezing conditions in order to avoid/limit the pressure inthe supply line and on the components located over this line. It mightbe as small as a bubble (in which case there generally are several ofthem) and can take various forms as it will be seen in more detailsbelow.

In the particular case where the system is used in a vehicle, the partforming the gas pocket can be installed in different locations in avehicle such as on top of the SCR tank, on top of the fuel tank, inwheel areas, on fuel or SCR filler pipes, etc. More than one partdefining a gas pocket may be connected to/comprised in the supply line.

According to a particular feature, at least a portion of the gas pocketis comprised in a substantially vertical portion of (or extending from)the supply line to benefit of the effects of gravity on the liquid. By“substantially vertical” is meant vertical or inclined enough (forinstance with an angle of at least 45°, preferably at least 60°) so asto be able to benefit of gravity effects.

In particular, this substantially vertical portion may consist in aportion of local enlargement of the diameter of the supply line.

Alternatively, the part defining the gas pocket may define several gaspockets thanks to the use of corrugations. Another alternative residesin the use of at least two coaxial communicating conduits, a firstconduit containing the liquid and another conduit containing air or anyother fluid that may be compressed to absorb the pressure stemming froma volume increase. These alternatives will be described below.

Thus, the system may comprise two coaxial conduits, the inner one ofwhich having an open end communicating with the interior of the outerconduit.

Thanks to these dispositions, in the event liquid contained in thesecond conduit freezes and expands upon freezing, the front side of theliquid/solid area moves forward (as the liquid is not compressible) andpushes against (compresses) the gas volume contained in the firstconduit.

According to a first sub-embodiment, the inner conduit comprises aclosed end and the gas pocket is present in said inner conduit with themain supply line forming the outer conduit.

Thanks to these provisions, in the event of a volume increase of theouter conduit, the front side of the liquid/solid moves inside theinternal line and pushes the gas, thus compressing it. Therefore, thegas contained in the inner conduit is compressed and absorbs pressureforces that could damage the outer conduit and other components of thesupply system.

According to a second sub-embodiment, the outer conduit comprises aclosed end and the gas pocket is present in said outer conduit.

The roles of the main supply line and the gas pocket are here reversedcompared to the previous embodiment.

According to another embodiment, the part forming the gas pocket is aline, appendix or branch emerging in said passage and extendingpreferably globally in the same direction as at least a part of thesupply line, without their axis coinciding. The diameter of this“dead-end” appendix may be larger than the diameter of thesupply/feeding line itself.

According to still another embodiment of the present invention, thesupply line comprises a corrugated part, the corrugations of which forma plurality of gas pockets.

An advantage of this solution is that in all areas where the line issubstantially horizontal (i.e. horizontal or slightly inclined: seeabove), air bubbles will be trapped within each upper part of thecorrugations. These bubbles will be compressed in the event of freezing.

The system may also comprise a gas trap in or between said at least onepart defining the at least one gas pocket and the rest of the supplyline in order to trap said gas.

When the supply system is placed within a moving vehicle comprising anexhaust system, such a disposition prevents the gas contained in thefeeding line from flowing towards the exhaust system by being sucked orfrom escaping out of the gas pocket when the vehicle is placed on aslope up.

According to a particular feature of this embodiment, the gas trap ispresent under the form of a siphon, in particular in the shape of aU-bend or an inverted U-bend. Other equivalent shapes (N-bend, labyrinth. . . ) can of course be implemented. Alternatively, the gas trap mayconsist of a sealed box (with inside bend shapes, labyrinth, etc . . . )with an inlet and outlet connected to the supply line, thus forming anadded element.

In the absence of separate (added) trap, the part forming the gas pocketshall be dimensioned and/or oriented so as to take the above-mentionedissues (sucking and inclination of the vehicle) into account and to actas a gas trap itself.

Hence, according to an embodiment of the invention, the at least onepart forming the gas pocket may be formed by an enlarged substantiallyvertical section of the supply line, extending between two transverseupper and lower sections and which is configured so as to enable theliquid to fall down to the bottom of the lower section while forming thegas pocket between the respective ends of this vertical section.Alternatively, the enlarged section may consist of a sealed box (withplunger, etc . . . ) having an inlet and an outlet connected to thesupply line.

With proper dimensioning of the enlargement and considering theviscosity of the mixture contained in the supply line and its low debitflow, this enlargement acts as a drip. Therefore a gas pocket can bemaintained, which can in turn be compressed in the event of freezing ofthe liquid.

According to a particular feature of the invention, the system maycomprise a pump, located inside or outside the tank. Alternatively,other solutions for supplying the outlet of the system with the liquidcan be foreseen (gravity, aspiration by exhaust gases, . . . ).

The pump is preferably a rotating pump (for instance a gear pump)preferably driven by a magnetically-coupled motor or a piston pumpactuated by a spring and a magnetic coil.

When such a pump operates in a supply system for an exhaust system of avehicle, the pressure in the supply line is generally adjusted to bewithin a range of about 1 and to about 5 bars (1 bar=1.10⁵ Pa), mostoften to about 5 bars.

The gas pocket is therefore compressed and the pressure in the supplyline must be reduced/relieved after the pump is stopped.

To reduce the pressure in the supply line as quickly as possible afterthe pump's stop (engine stop), preferably within a few minutes (5 to 10,in practice), so that the gas pocket compressed under the effect of thepressure returns to its initial volume (or almost to its initialvolume), to be able to be compressed again in the event of freezing, itis also proposed, according to particular features of the presentinvention:

to create at least one specific leakage in the structure of the pump(e.g. in its non-return valve) to make it possible for the liquid in thesupply line to return into the tank (the leakages in the today's pumpsare very limited and might in most of the cases be insufficient toreduce efficiently the pressure after the pump's stop); orto add a bypass connecting the supply line to the tank and provided witha valve, preferably an electrovalve, which when opened, makes itpossible for the liquid under pressure in the supply line to return tothe tank.In other words, the supply system advantageously comprises, moregenerally, means for reducing the pressure in the supply line,preferably means for returning liquid present in the supply line to thetank.

The supply of the liquid as well as its return to the tank, the casebeing, may be controlled by an engine control unit (ECU), some othercontrol unit incorporated into a vehicle (for example the fuel systemcontrol unit, FCSU) or a special-purpose control unit receivinginstructions/information from the ECU, from the FCSU or from some othercontrol unit incorporated into a vehicle.

A filter, which is intended to protect the pump from impurities ispreferably also foreseen, advantageously combined with the pump in acompact module, as described in International Application WO 2009/007405in the name of the Applicant.

According to another particular feature of the invention, the system maycomprise a pressure regulator, preferably integrated in the pump orconnected to the tank.

In particular, the pressure regulator may be a mechanical pressureregulator based on a ball and spring or plate and spring mechanism. Thepressure regulator may also consist of a pressure sensor combined withan electronic regulator.

Alternatively, for a piston pump, the pressure regulation may beobtained by a calibrated spring actuating the piston. In this case, thespring and piston push the liquid to the outlet of the pump.

In order to de-ice the liquid, the system may comprise a heater bandsurrounding the supply line or a resistive wire surrounding this line.Alternatively, the heater band or resistive wire is located inside thesupply line or inside the line wall thickness.

For simplicity's sake, the gas in the pocket(s) is air.

The invention also relates to a supply line suitable for a supply systemaccording to the invention, comprising either two coaxial conduits or anappendix emerging from it as described above.

The invention furthermore relates to a purification system for aninternal combustion engine, comprising a supply system as describedabove, for injecting an exhaust gas purification solution into anexhaust passage of the internal combustion engine.

The gas pocket(s) here also act as a dampener of the pressure pulses.

Advantageously, the gas purification solution is a reducing agentcapable of reducing the NOx present in the exhaust gases of the engine,such as an ammonia precursor in aqueous solution, preferably an aqueousurea solution.

Therefore, according to a particular feature of said purificationsystem, the exhaust gas purification solution may be an eutecticwater/urea solution. Solutions of AdBlue®, the urea content of which isbetween 31.8 and 33.2 wt % and 18 wt % of ammonia are particularlyefficient. The invention may also be applied to urea/ammonium formatemixtures in aqueous solutions, sold under the trademark Denoxium® andcontaining around 13 wt % of ammonia. The latter have the advantage offreezing from and below −35° C. as opposed to −11° C. with othersolutions.

Preferably, the tank is made in a material that is chemically resistantto the additive in question. In general such a material is metal orplastic. In the case of urea, polyamide or polyolefin resins, inparticular polyethylene, and more particularly HDPE or high-densitypolyethylene, are preferred.

Moreover, the gas pocket is dimensioned considering the expansion volumeof urea in freezing conditions in order to limit the pressure in thesupply line.

The invention also concerns the use of a system according to theinvention in a selective catalytic reduction system (SCR), preferablyusing an aqueous urea solution.

In this particular case, the gas pocket is dimensioned in order toavoid/limit the pressure in the feeding line when the urea is underfreezing conditions, but also on the injector, the pump, the quickconnectors, etc.

More generally, the supply system according to the present invention maybe used in any other context where a liquid which expands upon freezingis carried into practice.

The coaxial lines or corrugated conduct is (are) preferably made out ofa thermoplastic material, such as a PA (polyamide). The internal linecan also be made of a PE (polyethylene) or a PU (polyurethane).

For the coaxial lines, a good dimensioning includes an internal diameterof the internal line ranging between about 2 and about 5 mm, and aninternal diameter of the external line ranging between about 4 and about10 mm. The thickness of the lines preferably ranges between about 0.5and about 2 mm.

The present invention in possible embodiments is illustrated, in a nonlimitative way, by FIGS. 1 to 6.

FIG. 1 consists in a schematic sectional view of a system according tothe invention, in a first embodiment;

FIG. 2 consists in a schematic sectional view of a system according tothe invention, in a second embodiment;

FIG. 3 consists in a schematic sectional through view of a systemaccording to the invention, in a third embodiment;

FIG. 4A consists in a schematic sectional view of a system according tothe invention, in a fourth embodiment;

FIG. 4B schematically illustrates a variant of the enlargement of FIG.4A;

FIG. 5 consists in a schematic sectional view of a supply conduitaccording to a fifth embodiment of the invention, and

FIG. 6 schematically illustrates a variant of the gas trap of FIGS. 1 to5.

In these figures, identical reference signs denote identical or similarcomponents.

The system 1 of the embodiment presented in FIG. 1 comprises an SCR tank2 filled with a liquid 4 (an eutectic water/-urea composition in thepictured embodiment) and communicating with a supply circuit 6 through apump 8 for feeding the liquid 4 into the circuit and located here in thetank. It is combined with a filter (not illustrated on the drawings) ina compact module.

The supply circuit 6 comprises a connection 10 leaving the tank, whichin the particular embodiment shown in this Figure, communicates with abranch connected to a pressure regulator 12, located inside the tank.

In this embodiment, the pressure regulator is a mechanical pressureregulator based on a ball and spring or plate and spring mechanism.Alternatively, the pressure regulator may consist of a pressure sensorcombined with an electronic regulator.

Alternatively, for a piston pump, the pressure regulation may also beobtained by a calibrated spring actuating the piston. In this case, thespring and piston push the liquid to the outlet of the pump.

Upon leaving tank 2, the pump is connected to a coaxial line comprisingan outer conduit or external feeding line 14 surrounding an innerconduit or internal line 16, the latter forming an air pocket. Itcomprises, in this embodiment, a substantially vertical section betweentwo substantially horizontal sections (though other orientations maywork).

Both the internal and external lines are made out of a thermoplasticmaterial such as PA with internal diameters and thicknesses comprised inthe ranges defined above.

In addition, a heater band or resistant wire 17 is placed around theouter conduit 14 in order to de-ice the liquid contained therein whenrequired.

The internal conduit 16 has an open end 18 communicating with an outletof the external conduit 14 and an opposite closed end 20 located nearthe end of the external conduit 14 and near the connection 10.Therefore, in the event the liquid contained in the external feedingline freezes and expands, the front side of the liquid/solid area movesforward in the internal line 16 as the liquid is not compressible,compressing the gas volume contained therein. The compression of the gasthus allows for pressure reduction in feeding line 14 and on thecomponents of the supply system.

The location of open end 18 may vary. In the present embodiment, it islocated in the vicinity of an injector 24 that the lines lead to andwhich is adapted to inject the liquid 4 into the exhaust system of avehicle equipped with the supply system 1.

The presence of the air pocket also damps pressure pulses and reducesthe pressure range during the injection. The pressure regulation ingeneral is thus improved.

An optional air trap 22, consisting in the present embodiment in aninverted U-shaped portion of the coaxial lines, is placed downstream ofthe open end 18 and in the vicinity thereof. This trap prevents the gascontained in the internal line 16 from escaping therefrom.

Depending on the volume of the part forming the gas pocket, this trapcan be located elsewhere on the line.

The embodiment of FIG. 1 also comprises an optional bypass 24 connectingthe feeding line 14 to the tank 2 and equipped with an electrovalve 28for returning liquid under pressure present in the feeding line 14 tothe tank 2 once the pump 8 is stopped.

The air pocket which was compressed in the internal conduit 16 duringthe operation of the pump 8 can thus return to its initial state, inorder to be able of being compressed again in the event the liquidfreezes again.

Referring now to FIG. 2, another embodiment of the invention is shownwherein the roles of the external line 14 and the internal line 16 arereversed, the internal line 16 becoming the feeding line containing theliquid and the external line 14 becoming the part forming a gas pocket.

Referring now to FIG. 3, another embodiment of the invention is shownwhich includes providing the feeding line 30 with a branch 32 orappendix forming a gas pocket. This branch 32 may be located anywherebetween the injector and the gas tank 2 and extends in the presentembodiment along a part of the vertical intermediate section of thefeeding line 30 and then along a part of the horizontal section of thelatter proximate the tank 2. A very compact arrangement results fromthese provisions but other shapes and orientations for a dead-endappendix can be foreseen. herein this embodiment, the supply line 30 andthe appendix 32 are also surrounded by a heater band or resistive wire17.

The internal diameter of dead-end appendix 32 can be larger than the oneof feeding line 30: approximately 2 to 20 mm against approximately 2 to10 mm, for a thickness comprised approximately between 0.5 and 2 mm.

As for the previous embodiments, in the event of expansion of the liquidcontained in feeding line 30, caused by freezing, the front side of theliquid/solid moves forward in the branch 32, thus pushing the gascontained therein.

Referring now to FIG. 4, another embodiment of the invention is shownwhich includes an enlargement 34 of a feeding line 30 along a verticalportion of the latter. With proper dimensioning of the enlargement 34and considering the viscosity of the mixture contained in feeding line30 and its low debit flow (in practice 0.01 to 5 litres per hour withurea), this enlargement acts as a drip. Therefore a gas pocket can bemaintained, which can in turn be compressed in the event of freezing ofthe liquid.

In this embodiment, the enlargement 34 has an internal diameter ofapproximately 3 to 30 mm, whereas the rest of the feeding line 30 has aninternal diameter of approximately 2 to 10 mm, for a thickness ofapproximately 0.5 to 2 mm.

As shown on FIG. 4B, the enlargement 34 may also consist of a sealed box36 having an inlet 38 and an outlet 40 for connecting the box 36 to thefeeding line 30. The box 36 also comprises a plunging tube 42 connectedto the inlet 38 and descending up to the vicinity of the bottom of thegas pocket capacity formed by the box 36, so as to separate the gas fromthe liquid circulating in the feeding line 30.

An air trap 22 and/or a bypass 26 with an electrovalve 28 as in theembodiment described with reference to FIG. 1 are not represented onFIGS. 2 to 4A,4B, but such devices are preferably also present in theseembodiments.

FIG. 5 is a schematic sectional view of a conduit 44 which may replaceany of the coaxial conduits, dead-end appendix or enlarged section ofthe supply/feeding lines of the embodiments of FIGS. 1 to 4.

It consists in a corrugated conduit having a plurality of corrugations46 in the upper part of which air bubbles can be trapped for picking upa change of volume of the liquid, e.g. urea, in case of frost.

FIG. 6 shows another embodiment of the gas trap 22. It is implementedunder the form of a sealed box 48 comprising an inner wall 50 forming aU shaped channel.

This box 48 also comprises, for its connection to anyone of the feedinglines 14, 16, 30 described above, as an added element, an inlet 52 andan outlet 54.

Naturally, numerous modifications can be made to the exemplaryembodiments previously described without leaving the context of theinvention.

1-15. (canceled)
 16. A supply system for a liquid, comprising: a liquidtank, and a liquid supply line forming a passage for liquid from thetank to an outlet of the supply system, wherein the supply line includesat least one part configured to form at least one gas pocketcommunicating with the passage to take up a change of volume of theliquid in event of freezing.
 17. A supply system according to claim 16,wherein at least a portion of the gas pocket is comprised in asubstantially vertical portion of, or extending from, the supply line.18. A supply system according to claim 16, the supply line comprisinginner and outer coaxial conduits, the inner coaxial conduit including anopen end communicating with an interior of the outer coaxial conduit.19. A supply system according to claim 18, wherein the inner coaxialconduit comprises a closed end.
 20. A supply system according to claim18, wherein the outer coaxial conduit comprises a closed end.
 21. Asupply system according to claim 16, wherein the part forming the gaspocket is an appendix emerging in the passage.
 22. A supply systemaccording to claim 16, wherein the supply line comprises a corrugatedpart, corrugations of which form a plurality of gas pockets.
 23. Asupply system according to claim 16, wherein the at least one partforming the gas pocket is formed by an enlarged substantially verticalsection of the supply line, extending between two transverse upper andlower sections and which is configured to enable the liquid to fall downto a bottom of the lower section while forming the gas pocket betweenrespective ends of the vertical section.
 24. A supply system accordingto claim 23, wherein the enlarged section is formed by a sealed boxincluding an inlet and an outlet for connecting the box to the supplyline.
 25. A supply system according to claim 24, wherein the sealed boxcomprises a plunging tube connected to the inlet of the box andextending towards a bottom of the enlarged section to separate the gasfrom the liquid flow.
 26. A supply system according to claim 16, furthercomprising means for reducing pressure in the supply line, and means forreturning liquid present in the supply line to the tank.
 27. A supplysystem according to claim 26, wherein the means for returning liquidpresent in the supply line to the tank comprises at least one leakageformed in a structure of a pump or a bypass connecting the supply lineto the tank and including a valve, or an electrovalve.
 28. A supplysystem according to claim 26, further comprising a gas trap in orbetween the part forming at least one gas pocket and a rest of thesupply line to trap the gas.
 29. A supply system according to claim 28,wherein the trap is in a shape of a siphon, or has a U-bend, or aninverted U-bend.
 30. A supply system according to claim 28, wherein thetrap is formed in a sealed box including an inlet and an outletconnected to the supply line.